The present invention relates to a flow divider system used in a hydraulic circuit for a work machine including a boom cylinder and a bucket cylinder to divide a pressured oil drained from an one-boom chamber into a flow to an other-bucket chamber and a flow to a tank via an orifice and a flow diving valve.
Conventionally, it is known that there is provided a flow divider system used in a hydraulic circuit for a work machine including a boom cylinder and a bucket cylinder to divide a pressured oil drained from an one-boom chamber into a flow to an other-bucket chamber and a flow to a tank via an orifice and a flow dividing valve. See, for example, Japanese Patent Laid-Open Publication No. 10-219730 (page 4, FIGS. 1 and 2) (its corresponding U.S. Pat. No. 5,797,310), and Japanese Patent Laid-Open Publication No. 2-96028 (page 3, FIG. 1). A flow divider system disclosed in the former patent publication comprises a flow dividing valve 45 and orifices 75, 83. A flow divider system disclosed in the latter patent publication is comprised of a flow diving valve 18 including an orifice. The bucket-leveling function to maintain a bucket at a level position during a boom operation is materialized by these flow divider system supplying a return oil from the one-boom chamber to the other-bucket chamber.
In the flow divider system of the former patent publication, the orifice 75 is configured of a fixed orifice. Further, the orifice 83 comprising an opening 79 and a passage 81 is not configured either to be a variable orifice which can control its orifice degree automatically and adjustably during the operation of the flow divider system, even though it is structurally available for adjusting the orifice degree variably. As a result, this orifice functions just as a fixed orifice during the operation. Setting these fixed orifices 75, 83 at improperly reduced opening degrees may prevent an actuator from operating smoothly due to a restricted flow of pressured oil from a rod-side chamber of the boom cylinder. Accordingly, these fixed orifices need to be set at more proper opening degrees so as to provide such a smooth operation. Also, in the flow divider system of the latter patent publication, in which one is configured of a fixed orifice and the other is configured of a variable orifice, similar setting like the above may need to be applied to the fixed orifice as well.
Herein, there was a problem with such flow divider systems of the above-described patent publications that proper flow dividing may not be obtained in the event that the amount of oil drained from the rod-side chamber of the boom cylinder and flowing into the flow divider system becomes small enough under a certain condition which is different from a specified premise condition in setting the above preferable orifice opening degree. Namely, such small amount of pressured oil flowing could not provide a sufficient pressure raise at the upstream of the flow divider system, and thereby only small amount of oil may flow in a high-load side of diverged passage, while a large amount of oil may flow in a low-load side of diverged passage.
Herein, there are also other prior art disclosing similar flow divider system and a valve device of the same, such as Japanese Patent Laid-Open Publication No. 7-252857, U.S. Pat. Nos. 4,408,518 and 5,447,094.